MIT OpenCourseWarehttp://ocw.mit.edu 6.453 Quantum Optical Communication Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.November 18, 2008Optical and Quantum Communications Groupwww.rle.mit.edu/qoptics6.453 Quantum Optical CommunicationLecture 18Jeffrey H. Shapiro2www.rle.mit.edu/qoptics6.453 Quantum Optical Communication - Lecture 18! Announcements! Pick up random processes notes, lecture notes, slides! Continuous-Time Photodetection! Semiclassical theory — Poisson shot noise! Quantum theory — photon-flux operator measurement! Direct-detection signatures of non-classical light3www.rle.mit.edu/qopticsReal Photodetection Systems4www.rle.mit.edu/qoptics“Ideal” Photodetection System: Efficiency < 1h< 1PHOTO-DETECTOR5www.rle.mit.edu/qopticsClassical Field versus Quantum Field Operator! For Semiclassical Photodetection of Narrowband Light! Illumination is a classical photon-units positive-frequency field:! Short-Time Average Power on Detector:! For Quantum Photodetection of Narrowband Light! Illumination is a photon-units positive-frequency field operator:! Only non-vacuum frequency components are within6www.rle.mit.edu/qoptics! Semiclassical Theory: Given! is an inhomogeneous Poisson Counting Process! Rate function! Quantum Theory:Semiclassical versus Quantum Photodetection7www.rle.mit.edu/qopticsInhomogeneous Poisson Counting Process (IPCP)! Definition: is an IPCP with rate! Starts counting at zero:! Has statistically independent increments! Increments are Poisson distributed8www.rle.mit.edu/qoptics! Semiclassical Photocount and Photocurrent Mean Functions:! Semiclassical Covariance Functions:Mean and Covariance: Deterministic Illumination9www.rle.mit.edu/qoptics! Semiclassical Photocount and Photocurrent Mean Functions:! Semiclassical Covariance Functions:Mean and Covariance: Random Illumination10www.rle.mit.edu/qopticsMean and Covariance Functions: Quantum Case! Quantum Photocount and Photocurrent Mean Functions:! Quantum Covariance Functions:11www.rle.mit.edu/qopticsDirect-Detection Signatures of Non-Classical Light! Semiclassical Theory is Quantitatively Correct:! For coherent-state inputs! For inputs that are classically-random mixtures of coherent states! Sub-Poissonian Photon Counting:! Semiclassical theory:! Quantum theory:! Non-classical signature:12www.rle.mit.edu/qopticsDirect-Detection Signatures of Non-Classical Light! Photocurrent Noise Spectral Density for CW Sources:! Semiclassical Theory:! Quantum Theory:! Sub-Shot-Noise Non-Classical Signature:13www.rle.mit.edu/qopticsComing Attractions: Lecture 19! Lecture 19:Continuous-Time Photodetection! Noise spectral densities in direct detection! Semiclassical theory of coherent detection! Quantum theory of coherent detection! Coherent-detection signatures of non-classical
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